diff --git a/core/lib/Drupal/Core/SystemListing.php b/core/lib/Drupal/Core/SystemListing.php
index 20d95cb..bc56fc3 100644
--- a/core/lib/Drupal/Core/SystemListing.php
+++ b/core/lib/Drupal/Core/SystemListing.php
@@ -17,6 +17,13 @@
 class SystemListing {
 
   /**
+   * A list of profiles to search their directories.
+   *
+   * @var array
+   */
+  protected $profiles = array();
+
+  /**
    * Construct this listing object.
    *
    * @param array $profiles